Method of truing gears



Jan. s, 1929.

A. w. coPLAND ET AL mmo'n OF TRUING GEARS Filed April 10. 1922 ATTOPNEKPatented Jan. 8, 1929.

v I 1, 9 ,213 UNITED STATESPATENT OFFICE.)

ALEXANDER w. COPLAND nn MAXWELL I. MATHEWSON, or DETROTT, MICHIGAN,ASSIGNORS To DETROIT AND SECURITY TRUST COMPANY, or DETROIT, MICHIGAN,

A. CORPORATION OF MICHIGAN.

' METHOD or 'IRUING GEARS.

The invention relates to the art of truing gears and more particularlyto that part of it which is generally known, as lapping.

The lapping of gears has heretofore been effected by running two ormoregears in meshwith each other and with an abrasive material between theengaging surfaces or by similarly running a gear in-mesh with a rack.Where the only movement given to the gears is that of rotation abouttheir respective axes, the results obtained are not satisfactory. Thisis for the reason that the grinding is only produced where there is aslipping or sliding of one surface over another,,and inasmuchas thesliding upon each other'of the teeth of rotating intermeshing gears withthe commonly employed involute teeth is zero at the pitch circle andprogressively increases on each side of said circle with a maximum atthe crown of each tooth, it is evident that the grinding produced has atendency to change the tooth from its true involute form. With certainlapping methods a relative axial reciprocation has been imparted to theintermeshing gears, or to the gear and the rack in case a rack isemployed, in addition to the relative rolling, but this is alsodefective and inevitably results in distortion of the true involutetooth form because the effect includes that incident to the rolling asabove described.

In such a lapping or grinding operation as last referred to, the amountof grinding or abrading of a surface sliding in contact with another isdependent first, on the character of the abrasive material used; second,on the area of abrading surface that-is moved over each unit area of thesurface to be ground or trued; and third, the amount of pressure perunit area of contact. Accordingly, to pro duce uniform grinding on allportions of a surface contacting with the abrading surface there must beuniformity in abrasive mate improvement, the principles underlying thesame are illustrated diagrammatically in the accompanying drawings, inwhich:

Fig. 1 is a iagranimatic View showing the ntermeshing teeth of a spurgear and a lap in the form of a second spur gear and indicat-' mg by thediagonal shadin the relative widths of zones of surface W ich are trav-,ersed by the mating tooth during equal angu' lar movements.

Fig. 2 is a view similar to Fig. 1 showing the tooth of a spur gear inmesh with the teeth of a lap, the lap in this instance being 1n the formof aracli having straight sided teeth; f

7 Figs. 3and 4 are respectively a sectional elevation and a sideelevation of a gear in mesh with a rack surface forming a lap therefor,the section shown by Fig. 3 being taken on the line 3-3, Fig. 4.

Fig. 5 is a view similar to Fig. 3 showing a modified construction. 4

In Fig. 1 is shown a portion of a spur gear 1 having teeth 2, 2- ofinvolute form-in mesh with correspondingly shaped teeth 3 of a lap 4:,which in this instance is in the form of'asecond spur gear. The relativewidths of zones traversed by the mating tooth for equal angularmovements of either the gear or the lap are indicated by diagonalshading on the body of each tooth. It will be observed that these zonesvary in thickness from the roottowards the crown of each tooth. It willalso be observed that when two teeth are in mesh that the smallest zoneson one are adjacent the largest on the other. As, forinstance, zones atand b on the gear 1 are adjacent zones at and b on the lap 4. As thezones indicate the amount of surface traversed by the mating tooth forequal angular movements, the zones will have to traverse each otherduring a unit amount of such movement, which, dueto the difference inwidth of the contacting zones, will result in a relative sliding betweenthe contacting surfaces. It will also be observed that the intermediatezones are more nearly equal. This means that the relative slidingbecomes progressively less as the point of engagement approaches the midportions of the respective teeth. with zero sliding at the pitch line.-It will thus be seen thatthis relative sliding of the tooth surfaces isgreatest at the extremities of the intermeshing teeth and graduallydecreases to zero. at the pitch line.

%s the grinding away of the tooth surfaces occurs only where there isrelative sliding it follows that during tlie relative rotation of a spurgear in mesh with a lap in the form of a 5 second spur gear the.contacting surfaces will .be ground away more at their extremitles thanat the pitch line. Asstated, it has been proposed to combine an axialreciprocation of either the gear or the lap simultaneously 1 with therelative rotations, but this is also .defective as the sliding which isincident. to

the relative rotation above noted, is still present. J

In Fig. 2 we have shown a portion of a: spur I6 gear 5 with a tooth 6 ofinvolute form in mesh with the teeth 7, 7 of a lap 8 which 1n this caseis in the form of. an involute rack having straight sided teeth. Therelative widths of thezones traversed by the mating teeth for 2 equalangular movements of the ear to be und are indicated by diagonal sading, as

inthe previously described case. It will be observed however that thezones on the rack tooth are equal in width, The relative s1id 2 ingbetween the contacting teeth will be zero at the pitch line, as in thefirst instance but the variance in the relative slidin between i thecontacting surfaces above and elow the pitch line is not the same as inthe previously described exam le; however, it canbe readily ascertainedy comparing the widths of the zones on the adjacent surfaces of theintermeshing teeth. It has also been proposed -'to combine areciprocation of the rack parallel to the gear axis (or an axialreciprocation of the gear) simultaneously with their rela: tiverotation; but, as in the previous case, .there will still be adifference in the grinding effect due to the above noted sliding actioninco cident to the rotating movement.

If, during the relative rotation and simultaneous reciprocation of theintermeshing gear and lap, the length of the reciprocation of thelapping surfaces could be varied-in inverse proportion to the amount ofsliding incident to the rolling action, the area of abrad-- ing surfacemoving over each unitarea of the surface to be ground could be madeuniformthroughout. This supposed variable .50 reciprocation is notfeasible, but if, in place of a continuous surface on the lap tooth,this surface is interrupted or cut away with the width of theinterruptions varying in direct proportion to the amount of relativesliding,

5 the samecompensation ma be made for the unequal width of zones wituniform lengths of mi rocation.

As i ustrative of some of tli difierent ways in which the effectivegrinding area of the lap 00 can be varied, we have shownjn Figs. 3 and 4a-lap with its teeth modified in one way, and in Fi 5 aco'rresponding'lap with a distinctl erent modification.

gear wheel and 11 a lap in the form of a rack shown in' Figs. -3 and 4,10 represents a relation to which the gear wheel is reciprocated axiallywhile rolling in mesh therewith.

Any suitable means may be employed for pro- 11, 192&,to W. E. Hoke. Inthis modification, I

the teeth of the rack are interrupted or cut away by the V-shapedchannels 12. Obviously a lap of this form will have agrinding effect onthe gear tooth to be lapped that pro-v gressively increases from'theroot of the gear tooth toward its crown.

In Fig. 5 the arrangement of lap 21 and gear 20 is similar to Figs. 3and 4, the difi erence being that the interruptions or cut-away portions22 of the lap in this instance are dove-tailed in shape with the widthof interruption greater. at the base of the rack tooth than at thecrown. Obviously this construction has an opposite effect to that shownin Figs. 3 and 4. In utilizing our invention one first prede terminesthe amount of relative sliding occurring between the contacting surfacesofthe particular 'form of'gear and lap teeth in-' volved incident totheir relative rotation, and

- then forms the lap so that the width of the interruptions or cut-awayportions will-in suitable roportion be greater at the point where theargest amount of sliding occurs and smaller where the lesser amount ofsliding ocours; It will thus be seen that through the use of our methodthe contacting areas of the tion to the amount of relative slidingetween --the contacting gear and lap surfaces incident to the relativerotating movement, to com ensate for that variable-sliding. Otherthingsrotating movement, ut in practice this strict roportionality may.bemodified somewhat v y the fact that variation of the contacting areastends to affect the other two determinmg factors, namely, the pressureper unit incident to the relative area and the effect of the abrasive,and it is desirable to take this into account in determmmg the propervariation of the contact areas, as can readily be done if on first trifi 'III the desired compensation is notfull secured.

In considering the action of the m 'fied lap, it is to be borne inmindthat the abrasive action is mutual, afiecting the lap as well as thegear.

is applicable in instances where it is desired to produce a uniformofthe gear tooth surfaces. is desira le when the Themethod asspecifically' described'above original contour of the geartooth issubstantially correct, and all that is needed is. a smooth finishedsurface. "However, our invention is also the originaltoo surface notatplplicable where lapping surface are varied in suitable tpropor-erectly formed, asfor instance where there interruptions or cut-awayportions of the lap tooth would be so formed as to compensate for therelative slidin referred to above and at the same time so ormed as togrind away more surface at the point'where the excess material occurs.In order to produce this combined action of compensating for therelative sliding and the difierentlal grinding the width ofinterruptions at the base of the lap toothwould be relatively smaller soas to present a larger area of abrading surface ing comp to contact withthe crown of the tooth and thus correct the original defect in the toothform, while at the same time, the-lapping produces the smoothly finishedsurface desired. Thus by properly formingl the interruptions in the lapany desire grinding efiect may be; roduced,'siich for instance, asuniform grin ing where the tooth form is originally correct ordifferential grinding where the original tooth form needs modification.v

While we have described our method as applied to the grinding of gears,it is obvious that it is equally ap licable to the grinding d circularbodies; also, that it is equally applicable to the grinding of internaland externalsurfaces.

What we claim is:

1. In a method of grinding gears by imparting simultaneously relativerotation and axial reci rocation to a gear and a 1a ;l havementaryintermeshing teet the provision and use of a lap so formed that itsabrasive area which is brought into contact with the gear teeth saidreciprocation varies during the relative movement of the gear and lap insuitable proportion to the amount of relative sliding between thecontacting gear and lap surfaces incident to the relative rotation ofthe gear and lap to compensate for said sliding.

' 2.. In a met 0d of grinding gears by imparting simultaneously relativerotation and axial reciprocation to a gear and a lap havingcomplementary intermeshing teeth; the provision and use of a lap soformed that its abrasive area which is brought into contact with thegear teeth by said reciprocation varies during the relative movement ofthe gear and lap in suitable proportion to the amount of relativesliding between the contacting gear and lap surfaces incident to therelative rotation of the gear and lap and to 1 the amount of excessmaterial to be removed to compensate for said sliding and for thesaidexcess material.

3. The method of finishing surfaces of gear teeth to predeterminedcontours which consists in lmparting simultaneously relative rotationand axial reciprocation to the gear and a lap having tooth-like lappingsurfaces which are in abrasive contact with the gear and .formed to havetheir surface areas which are brought into abrasive engagement with thegear teeth by .the said reciprocation varied by the combined rotationand reciprocation in suitable proportion to the amount ofrelative'slidin' between the contacting gear and lap sur aces incidentto the sai rotation to compensate for said sliding.

4. The method of grinding toothed bodies teeth of the body with atoothed a rading tool, causing between the body and-tool a rel-.

ative an ular motion in the plane of the gear body and also a relativetransverse motion in an axial plane of the gear body and by the combinedangular and transverse motion varying the area of abrasive contact ofthe radial faces of the tool with the teeth of the gear incident to saidtransverse motion in a predetermined proportion to the slip or relativesliding between the teeth of the body and the too'i due to the saidangular motion.

In testimony whereof we afiix our signatures.

ALEXANDER W. COPLAND. MAXWELL I. MATHEWSON.

